Here discuss injection molding mold design process, see principle of making a mold design.
- Part and counter part design review (2D/3D)
- Dimension categorization (from product 2D)
To concentrate the critical/important dimension instead of general/reference dimension. Use time more efficient and shorten the lead time.
- Shrinkage consideration (part thickness/x-axis/y-axis)
Most of the raw material has 2 direction shrinkage rates, and the rate was tested in a controlled setting and environment (see test method in B-7). The actual shrinkage rate shall be adjusted according to expected part design. see example below:
We are making a mold design with following elements:
- Part has thickness 1 mm in average.
- Raw material with shrinkage rate 15/1000 (the test piece has a thickness 3 mm in average).
The shrinkage rate of raw material changes according to the actual part design. In this case, since the expected part design thickness is 1/3 compared to the test piece of raw material. The shrinkage applied in mold design shall be adjusted accordingly. The shrinkage of this mold design shall be 5/1000 in the beginning. According the trial shot result, designer then modify the mold design at required area.
- Precaution on part 3D (reduce plastic)
To reduce steel in mold is very easy, but it is very difficult to increase.
This activity mostly being applied into the critical/important area (both in the dimension/profile perspective). The major purpose of this activity is preventing welding in mold. Welding is a process really really harmful to steel, it shall be absolutely prevented in any mold.
The idea of precaution on part 3D is to reduce the profile of of the important area, it leads to less plastic and more steel at the subject area in mold. It generates a mold design which is easier for modification after trial shot. This lower the risk of welding requirement or change mold part, and schedule delay.
- Establish mold 3D design by following parting line and mold layout.
- Establish mold 2D by projection of mold 3D
- Establish mold part design by separating mold 2D/3D design
- Establish BOM
- Establish mold part manufacturing/machining design
Most of the concern shall be discussed and solved in DFM, if there is any found in between the mold design phase, discuss with engineering/sales/customer…etc.